1. Field of the Invention
The present invention relates to a valve unit and an inkjet print head used in an inkjet printing apparatus.
2. Description of the Related Art
In a serial scan type inkjet printing apparatus that prints an image by moving a carriage on which a print head is mounted, there are two ink tank constructions: an on-carriage tank construction in which an ink tank is mounted on the carriage and an off-carriage tank construction in which the ink tank is located on the body of the printing apparatus, not on the carriage. With the on-carriage tank construction, it becomes increasingly difficult to raise a printing speed as the ink tank capacity increases. With the off-carriage tank construction, on the other hand, the carriage can be reduced in size and weight even as the ink tank capacity increases.
In a printing apparatus with such an off-carriage tank construction, the print head needs to be applied with an appropriate negative pressure to supply ink from the ink tank to the head. Japanese Patent No. 3606282 describes a construction in which, to realize such an ink supply, a valve unit with a self-sealing function is mounted on the carriage. This valve unit has a pressure adjusting mechanism that comprises a pressure chamber to receive ink from the ink tank through a supply path, a valve to open and close the supply path and a flexible film that deflects according to the negative pressure produced as the ink volume in the pressure chamber decreases. The displacement of the flexible film is directly transmitted to the valve for its open/close operation.
To minimize the size of the carriage, a construction having two pressure adjusting mechanisms in one valve unit is described in U.S. Pat. No. 7,556,362. On one side surface of the valve unit there is a flexible film that inflates outwardly according to the pressure in a pressure chamber of one of the pressure adjusting mechanisms. On the other side surface of the valve unit another flexible film is installed which inflates outwardly according to the pressure in a pressure chamber in the other pressure adjusting mechanism.
As described in U.S. Pat. No. 7,556,362, the provision of two pressure chambers in one valve unit can halve the number of valve units required, which in turn results in a corresponding reduction in the size of the carriage. However, since the outwardly inflating flexible films are installed on both side surfaces of the valve unit, the valve unit necessarily increases in its width.
Particularly when the outward deflection of the flexible film is set large, this greatly affects the widthwise size of the valve unit. Further when a plurality of valve units are mounted on the carriage, the carriage necessarily becomes large. Furthermore, during a valve unit assembly or during a replacement and reinstallation of the valve unit, a precaution needs to be exercised to avoid interference between the adjoining valve units. This makes it necessary to secure a sufficient clearance between the adjoining valve units by taking into account the outward deflection of their flexible films, which in turn increases the installation space of the valve units. Therefore, for a reduced size of the valve units, there has been no alternative but to reduce the size of the pressure chambers formed inside the flexible films, restricting the function of the pressure adjusting mechanism.